The prostate cancer market is about to get very interesting. Medivation and Astellas expect interim data by the end of the year from their Prevail trial testing Xtandi in patients who haven't been given chemotherapy. Xtandi is currently only approved for use after chemotherapy, leaving Johnson & Johnson's Zytiga the pre-chemo market essentially all to itself.

David predicts Xtandi can take half of the market in less than a year, which sounds a little ambitious. But as he points out, it depends on the data, which we haven't seen yet. Also, it's easier to penetrate an oncology market with an established player than one for a chronic condition because capturing newly diagnosed patients is key. It's unlikely you'll see a mass switch from patients currently taking Johnson & Johnson's Zytiga no matter how good the data are, but the important thing to watch is how well Medivation and Astellas are able to convince doctors to prescribe the drug to their new patients.

The graph speaks for itself and shows just how hard it is to launch a drug. Sure, there are some drugs in the under-$20-million category that are launching into small markets and will never be blockbusters, but there are also plenty of challenges that drugmakers face -- including stiff competition, doctors' reluctance to prescribe new therapies, and getting coverage from payers -- even when they're launching into multibillion-dollar markets.

Investors need to keep that in mind when valuing biotechs on the verge of launching drugs.

Keeping in mind Zach's comment about critical thinking, of course.

. @adamfeuerstein If they stop Reduce-It, they should close the company and none of the executives should ever work in biotech again. $AMRN

As a scientist, I understand the argument. I'd like to know if Amarin's Vascepa not only improves triglyceride levels but also improves cardiovascular outcomes -- the purpose of the Reduce-It trial.

But Amarin's management is beholden to its shareholders, not to scientific curiosity. If the biotech decides the cost of continuing the trial -- including the cost of raising additional capital, which could be expensive -- doesn't justify the risk-adjusted expected value from a positive clinical trial, it's not in shareholders' best interests to continue the trial.

There are certain ethical issues with stopping the trial, but if the FDA is arguing that results from other trials testing triglyceride-lowering drugs make it unlikely that Reduce-It will succeed, it seems reasonable to end the trial. Patients can still get the drug off label if they believe it's helping them.

$SRPT Are they serious?The pIII confirmatory study to be OPEN LABEL and use the 6MWT as primary endpoint? Do they have so little confidence?

Sarepta Therapeutics is in a bit of a tight spot designing the phase 3 trial for its Duchenne muscular dystrophy drug eteplirsen. It's hard to argue from the phase 2 data that eteplirsen doesn't work -- it might even get approved using that data alone -- so running a trial with a placebo control could be considered unethical if you assume the drug works. It might even be impossible to run that kind of study if eteplirsen is approved while the phase 3 trial is still running because many patients in the trial will dropout and take the approved product rather than risk being in the placebo group.

Sarepta Therapeutics is getting around the issue by having a matched control group of patients with Duchenne muscular dystrophy who have mutations that eteplirsen wouldn't be expected to help. While it's a reasonable control group, the trial is open label -- that is, everyone knows who's getting the drug and who isn't. The trial will assess how far the patients can walk in six minutes, which measures not only how well the drug is working, but, to some extent, how much effort the patient wants to put into the test. It's reasonable to assume that patients getting a drug that they believe will help them are likely to work much harder during the six-minute walk test than those who know they're in the control group.

That's going to skew the results in eteplirsen's favor, but I think Sarepta is doing it because of the ethical and practicality issues, not because management has little confidence in the drug. Fortunately, Sarepta seems to have a good relationship with the FDA, so I'm sure whatever trial design the company settles on will be signed off by the agency.

As a reminder, tweet me at @BiologyFool if you see an educational or entertaining tweet that you think should be included in next week's roundup. Admittedly, I can't see every interesting tweet out there.

Look for game-changing biotechs in any marketThe best way to play the biotech space is to find companies that shun the status quo and instead discover revolutionary, groundbreaking technologies. In The Motley Fool's brand-new FREE report "2 Game-Changing Biotechs Revolutionizing the Way We Treat Cancer," find out about a new technology that big pharma is endorsing through partnerships, and the two companies that are set to profit from this emerging drug class. Click here to get your copy today.